The present invention relates to a thermal protector and more particularly a thermal protector of the type which is reset by removing the unpressed voltage so as to close the contacts after the latter are opened as the environmental temperature rises to a predetermined level.
In general the thermal protectors have a stationary electrode and a movable electrode having a heat responsive element such as bimetal. When the environmental temperature rises to a predetermined level, the stationary and movable electrodes are moved away from each other so as to interrupt the current flowing into a load which is connected to a power source through the thermal protector. They are widely used as safety devices for preventing overheating of various types of electrical machinery and equipment.
Resettable type thermal protectors wherein the stationary and movable electrodes are bridged with a heat sensitive resistor with a positive thermal coefficient are known. More particularly, the heat responsive resistor element is inserted into a recess formed in the movable electrode and is pressed against it under the force of a leaf or plate spring extending from the stationary electrode so that the heat responsive resistor element may be securely clamped between them.
The thermal protector of the type described, however, has the disadvantage that since the heat responsive resistor element is mechanically clamped between the stationary and movable electrodes as described above, the thermal protector is not reliable and dependable in operation. It cannot be certain that the thermal protector will precisely open its contacts at a predetermined environmental temperature and the thermal protector exhibits less resistance to vibration.